1. Field of the Invention
The present invention relates to a display device, and more particularly to a signal line of a touch panel display device and method of forming the same.
2. Description of the Related Art
In general, a touch panel device is a computer peripheral that is commonly installed on a display surface of an image display device such as a cathode ray tube (CRT), a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an electro-luminescence device (ELD) so that while looking at the image display device, a user applies pressure on the touch panel to enter predetermined information into the computer.
FIG. 1 is a perspective view of a touch panel display device and a liquid crystal display panel according to the related art. In FIG. 1, the touch panel display device includes a touch panel 2, a liquid crystal panel 1, and a backlight 3. The touch panel 2 is electrically connected to a computer system 5 via a touch controller 4 by signal lines. During operation of the touch panel display device, if a top of the touch panel 2 is contacted with more than a specific pressure, a voltage value of the contact position is calculated by the touch controller 4, thereby calculating coordinates of the contact position.
FIG. 2 is a cross sectional view of the touch panel display device and the liquid crystal display panel of FIG. 1 according to the related art. In FIG. 2, a liquid crystal display panel 1 is located between an upper polarized sheet 4A and a lower polarized sheet 4B, and the touch panel 2 is placed on the upper polarized sheet 4A. The liquid crystal panel 1 includes liquid crystal material 14 and a ball spacer 5 interposed between a lower glass substrate 3A and an upper glass substrate 3B. A gate line 6, an insulation film 8, a pixel electrode 10A, and a first alignment film 12A are sequentially formed on the lower glass substrate 3A. The upper glass substrate 3B has a black matrix 16, a color filter 18, a common electrode 17, and a second alignment film 12B sequentially formed on a bottom surface thereof. The ball spacer 5 is sprayed on a first alignment film 12A before the upper glass substrate 3B is bonded with the lower glass substrate 3A. The upper glass substrate 3B and the lower glass substrate 3A are separated by the ball spacer 5 to be maintained with a specific gap. That is, the spacer 5 uniformly maintains the gap between the upper glass substrate 3B and the lower glass substrate 3A, thereby maintaining a uniform thickness of the liquid crystal material 14.
The touch panel 2 includes a spacer 28 formed between a lower substrate 20 and an upper substrate 24. A first electrode layer 26 is formed on the surface of the lower substrate 20, and a second electrode layer 27 is formed on a bottom surface of the upper substrate 24. The second electrode layer 27 is electrically shorted with the first electrode layer 26 when the upper substrate 24 is pressed with a stylus pen or a finger, to generate a current or voltage level signal that changes in accordance with the pressed position. Accordingly, the first electrode layer 26 and the second electrode layer 27 are formed by printing silver Ag on transparent conductive material that has good transmittance, and has a low resistance. For example, the first electrode layer 26 and the second electrode layer 27 include indium-tin-oxide ITO, indium-zinc-oxide IZO, and indium-tin-zinc-oxide ITZO.
FIG. 3 is a plan view of an electrode and a signal line of the touch panel display device of FIG. 2 according to the related art. In FIG. 3, an upper plate of the touch panel 2 includes X-axis electrodes 27A and 27B formed along an edge thereof along a vertical direction, and signal lines 28C and 28D are derived from a center of the X-axis electrodes 27A and 27B for supplying the current or voltage level signal to the touch controller 4. In addition, a lower plate of the touch panel 2 includes Y-axis electrodes 26A and 26B formed along an edge thereof a long a horizontal direction, and signal lines 28A and 28B are derived from a center of the Y-axis electrode 26A and 26B for supplying the current or voltage level signal to the touch controller 34.
FIG. 4 is a perspective view of two separate substrates of the touch panel display device of FIG. 3 according to the related art. In FIG. 4, the signal lines 28A, 28B, 28C, and 28D include a tail part 29 and an electrode extension connected to the electrodes 26A, 26B, 27A, and 27B. If the two substrates are bonded together as above, then the electrodes 26A, 26B, 27A, and 27B, and the signal lines 28A, 28B, 28C, and 28D are arranged together.
However, in the event of extending the signal lines 28A, 28B, 28C, and 28D to one side of the touch panel 2, one or more signal lines are formed in the four directions of the touch panel 2 like A, B, C, and D of FIG. 3. Accordingly, the touch panel 2 needs a space for the signal lines to be laid besides a display area surrounded by the electrodes 28A, 28B, 28C, and 28D. Thus, there are problems in that the pattern forming the signal lines of the touch panel lessens the efficiency in using the substrate, thereby increasing costs and the overall size of the applied system.